Much more silently than it came into the world, music search and sharing site Social.FM has gone back out — leaving what users it had to retreat to Pandora, iLike or one of the other, more successful music sites on the Internet.

The news was discovered by GigaOm based on a tip, who went on to find that the company’s site and widgets have all gone down. Formerly known as Mercora, the company had taken about $5 million from Norwest Venture Partners.

Social.FM was started back in 2004 by the former CEO of McAfee.com, and initially attracted attention to itself by being one of the few music sites at the time to get funding. At one point, it was hosting dinners for press to point out the differences between itself and Grokster, which was embroiled in a legal battle with MGM.

Attention is a double-edged sword, though. Within a couple years, we were awash in music startups. Earlier this year, VentureBeat put together a list of 38 of those companies, although it certainly wasn’t comprehensive — in a fit of foresight, we even left out Social.FM.

On review, that list is already getting pared down: Ezmo has shut down, and RadioBlogClub’s site is on hiatus (although the software can be downloaded). The rest appear to be functioning, but something tells me the music won’t keep playing forever.

More news, commentary, and predictions from The Industry Standard:

• Analysis: How MySpace Music could beat iTunes
• Special Feature: Where are they now? The Industry Standard tracks down 10 dot-coms from the Web bubble of the late 1990s